The present disclosure pertains to the art of medical diagnostic imaging, such as to computerized tomographic (CT) scanners. The disclosure finds particular application in conjunction with cooling systems associated with CT scanners and will be described with particular reference thereto. It will be appreciated, however, that the invention has broader applications and may be advantageously employed in other environments.
When a CT scanner is in operation, an X-ray beam rotates rapidly in a patient examination region. An X-ray tube rotates continuously around the examination region and causes the beam to so rotate. The X-ray tube generates a significant amount of heat as well as the X-rays. Because the x-ray sensors or detectors are heavily affected by absolute and temperature differences during calibration and scanning, a thermal control system is necessitated. X-ray sensors typically have 4 dominate temperature dependent properties that require tight temperature control systems: 1) Electronic gain temperature coefficient or gain shifts from the photo diode and A to D circuits, 2) offset drift of photo diode & A to D circuitry, which results in change of zero current reference during a scan, 3) Current leakage due to photo diode R shunt resistance which is a function of absolute temperature, and 4) Light output variation of scintillator material as function of temperature. These 4 temperature dependent properties translate into need for temperature control system to limit maximum photo diode temperature, minimal temperature change between calibration of the machine and scanning with machine, and lastly extremely small temperature change within a scan (data acquisition period). Failure to control absolute temperature and temperature change will result in image artifacts and loss of image resolution.
One available CT scanner cooling system uses an air conditioned sealed gantry to maintain radiation detectors at a proper working, temperature. CT scanner cooling systems of the type to which this invention pertains have included air conditioning units housed within CT scanner gantries. Other cooling systems employed in presently available imaging systems include liquid cooling systems and tight gantry system air temperature controls and/or electronic temperature correction schemes. Such cooling systems have been employed to cool radiation detectors, as well as other temperature-sensitive components associated with the CT scanners and other imaging devices.
The use of air conditioning systems in connection with CT scanners has several drawbacks. Gantry air conditioning systems are housed outside of the CT gantry due to size and audible noise of the air conditioning units. Typically the air conditioning units are vapor compression based or use hospital chilled water in a liquid to liquid heat exchange. These units add hardware cost, installation complexity, require significantly more electrical power in addition to CT scanner and increase overall system maintenance. Additionally vapor compression systems are significant audible noise sources and thus typically are placed outside of scan room further complicating siting of CT machine.
The use of liquid cooled gantries and/or electronic temperature correction schemes also have drawbacks, as they add complexity and cost to the system. Further, liquid cooling, systems add reliability issues, such as leakage problems. Temperature corrections, although favorable with respect to cost, induce loss of imaging accuracy.
Currently available data acquisition systems (DAS) cooling is also done with air cooled systems employing multiple fans. Such systems include that described in U.S. Pat. No. 7,102,308.
Thermal management of CT detector systems is required to prevent image artifacts or errors and to enable high quality images (improved signal to noise ratio) and for the life of the electronic components. As gantries become smaller and components more tightly integrated, coupled dynamics and flows inside a gantry become complicated and thermal management becomes more difficult. Thus, improved cooling systems are needed to provide sufficient control over the temperature for use in some imaging systems to maintain even and consistent temperature control and good image reconstruction quality.